Document updates to mod_filter.

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    <dl>

    <dt>Declare Filters</dt>

    <dd>The <directive module="mod_filter">FilterDeclare</directive> directive

    declares a filter, assigning it a name and a dispatch criterion.</dd>

    declares a filter, assigning it a namen.</dd>

    <dt>Register Providers</dt>

    <dd>The <directive module="mod_filter">FilterProvider</directive>

    directive registers a provider with a filter. The filter must have

    directive registers a provider with a filter. The filter may have

    been registered with <directive module="mod_filter"

    >FilterDeclare</directive>. The provider must have been

    >FilterDeclare</directive>; if not, FilterProvider will implicitly

    declare it with the default level AP_FTYPE_RESOURCE. The provider

    must have been

    registered with <code>ap_register_output_filter</code> by some module.

    The final argument to <directive module="mod_filter"

    >FilterProvider</directive> is a match string, that will be checked

    against the filter's dispatch criterion to determine whether to run

    this provider.</dd>

    The remaining arguments to <directive module="mod_filter"

    >FilterProvider</directive> are a dispatch criterion and a match string.

    The former may be an HTTP request or response header, an environment

    variable, or the Handler used by this request.  The latter is matched

    to it for each request, to determine whether this provider will be

    used to implement the filter for this request.</dd>

    <dt>Configure the Chain</dt>

    <dd>The above directives build components of a smart filter chain,

    <dd>A simple case of using <module>mod_filter</module> in place of

    <directive module="core">AddOutputFilterByType</directive>

    <example>

      FilterDeclare SSI Content-Type<br/>

      FilterProvider SSI INCLUDES $text/html<br/>

      FilterDeclare SSI<br/>

      FilterProvider SSI INCLUDES resp=Content-Type $text/html<br/>

      FilterChain SSI

    </example>

    </dd>

    <dd>The same as the above but dispatching on handler (classic

    SSI behaviour; .shtml files get processed).

    <example>

      FilterDeclare SSI Handler<br/>

      FilterProvider SSI INCLUDES server-parsed<br/>

      FilterProvider SSI INCLUDES Handler server-parsed<br/>

      FilterChain SSI

    </example>

    </dd>

    <dt>Emulating mod_gzip with mod_deflate</dt>

    <dd>Insert INFLATE filter only if "gzip" is NOT in the

    Accept-Encoding header.

    Accept-Encoding header.  This filter runs with ftype CONTENT_SET.

    <example>

      FilterDeclare gzip req=Accept-Encoding<br/>

      FilterProvider gzip inflate !$gzip<br/>

      FilterDeclare gzip CONTENT_SET<br/>

      FilterProvider gzip inflate req=Accept-Encoding !$gzip<br/>

      FilterChain gzip

    </example>

    </dd>

    <dd>Suppose we want to downsample all web images, and have filters

    for GIF, JPEG and PNG.

    <example>

      FilterDeclare unpack Content-Type<br/>

      FilterProvider unpack jpeg_unpack $image/jpeg<br/>

      FilterProvider unpack gif_unpack $image/gif<br/>

      FilterProvider unpack png_unpack $image/png<br/>

      FilterProvider unpack jpeg_unpack Content-Type $image/jpeg<br/>

      FilterProvider unpack gif_unpack Content-Type $image/gif<br/>

      FilterProvider unpack png_unpack Content-Type $image/png<br/>

      <br />

      FilterDeclare downsample Content-Type<br/>

      FilterProvider downsample downsample_filter $image<br/>

      FilterProvider downsample downsample_filter Content-Type $image<br/>

      FilterProtocol downsample "change=yes"<br/>

      <br />

      FilterDeclare repack Content-Type<br/>

      FilterProvider repack jpeg_pack $image/jpeg<br/>

      FilterProvider repack gif_pack $image/gif<br/>

      FilterProvider repack png_pack $image/png<br/>

      FilterProvider repack jpeg_pack Content-Type $image/jpeg<br/>

      FilterProvider repack gif_pack Content-Type $image/gif<br/>

      FilterProvider repack png_pack Content-Type $image/png<br/>

      &lt;Location /image-filter&gt;<br/>

      <indent>

        FilterChain unpack downsample repack<br/>

<directivesynopsis>

<name>FilterDeclare</name>

<description>Declare a smart filter</description>

<syntax>FilterDeclare <var>filter-name</var> [req|resp|env]=<var>dispatch</var>

    <var>[type]</var></syntax>

<syntax>FilterDeclare <var>filter-name</var> <var>[type]</var></syntax>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>Options</override>

    <directive module="mod_filter">FilterChain</directive> and

    <directive module="mod_filter">FilterProtocol</directive> directives.</p>

    <p>The second is a string with optional <code>req=</code>,

    <code>resp=</code> or <code>env=</code> prefix causing it

    to dispatch on (respectively) the request header, response

    header, or environment variable named.  In the absence of a

    prefix, it defaults to a response header.  A special case is the

    word <code>handler</code>, which causes <module>mod_filter</module>

    to dispatch on the content handler.</p>

    <p>The final (optional) argument

    is the type of filter, and takes values of <code>ap_filter_type</code>

    - namely <code>RESOURCE</code> (the default), <code>CONTENT_SET</code>,

<name>FilterProvider</name>

<description>Register a content filter</description>

<syntax>FilterProvider <var>filter-name</var> <var>provider-name</var>

    <var>match</var></syntax>

 [req|resp|env]=<var>dispatch</var> <var>match</var></syntax>

<contextlist><context>server config</context><context>virtual host</context>

<context>directory</context><context>.htaccess</context></contextlist>

<override>Options</override>

    <p>This directive registers a <em>provider</em> for the smart filter.

    The provider will be called if and only if the <var>match</var> declared

    here matches the value of the header or environment variable declared

    as <var>dispatch</var> in the <directive module="mod_filter"

    >FilterDeclare</directive> directive that declared

    <var>filter-name</var>.</p>

    as <var>dispatch</var>.</p>

    <p><var>filter-name</var> must have been declared with

    <directive module="mod_filter">FilterDeclare</directive>.

    <p>

    <var>provider-name</var> must have been registered by loading

    a module that registers the name with

    <code>ap_register_output_filter</code>.</p>

    <code>ap_register_output_filter</code>.

<!-- Placeholder; this is totally broken as of now

     , or declared with

    <directive module="mod_filter">FilterDeclare</directive>

    (or implicitly with another

    <directive module="mod_filter">FilterProvider</directive>).

-->

    </p>

    <p>The <var>dispatch</var> argument is a string with optional

    <code>req=</code>, <code>resp=</code> or <code>env=</code> prefix

    causing it to dispatch on (respectively) the request header, response

    header, or environment variable named.  In the absence of a

    prefix, it defaults to a response header.  A special case is the

    word <code>handler</code>, which causes <module>mod_filter</module>

    to dispatch on the content handler.</p>

    <p>The <var>match</var> argument specifies a match that will be applied to

    the filter's <var>dispatch</var> criterion.  The <var>match</var> may be

    <tr><th>Character</th><th>Description</th></tr>

    <tr><td><em>(none)</em></td><td>exact match</td></tr>

    <tr><td><code>$</code></td><td>substring match</td></tr>

    <tr><td><code>/</code></td><td>regexp match</td></tr>

    <tr><td><code>/</code></td><td>regexp match (delimited by a second <code>/</code></td></tr>

    <tr><td><code>=</code></td><td>integer equality</td></tr>

    <tr><td><code>&lt;</code></td><td>integer less-than</td></tr>

    <tr><td><code>&lt;=</code></td><td>integer less-than or equal</td></tr>